How to introspectively modify nodes from Python
Blender data does not have a __dict__ because it doesn't persistently store a Python object for all data. That would be very memory inefficient.

Set value for built-in and user defined properties of the node type:

setattr(node, property_name, property_value)


Set node input socket value:

node.inputs[socket_name].default_value = socket_value


For properties for one specific node you can use the method mentioned in the other answer:

node[property_name] = property_value